Light sources are evolving toward assemblies of light emitting elements such as light emitting diodes which are known in the art as LED's. Assemblies of LED's are being used or will be used in many high volume applications because they produce substantial light in proportion to the power consumed, are long lived and are extremely reliable. One such application is light sources for vehicles, such as headlights, taillights and directional signal lights. Other applications include replacements for florescent and incandescent lights and the like.
High output LED's, particularly when a large number are used on a common support, have a problem because they produce a significant amount of heat and the current generation of LED's begin to lose brightness when they are hotter than about 100° C. There are two current approaches to dissipate heat in commercially produced high output LED assemblies. The first is to apply the LED's to a circuit board which is glued to an aluminum heat sink. This is not a particular efficient technique for dissipating heat because the circuit board and the glue are tolerably good thermal insulators thereby insulating the heat source from the heat sink. The second is to apply the LED's to an epoxy layer bonded to an aluminum plate. The epoxy layer acts as an electrical insulator for electrical reasons but it is likewise a good thermal insulator thereby insulating the heat source from the heat sink.
It has been proposed in U.S. Pat. No. 5,857,767 to apply LED's to an aluminum heat sink which is anodized or which is coated with an electrically insulating layer by using a thermally conductive adhesive, i.e. an adhesive having dispersed metallic particles. There are several problems with this approach. First, conductive adhesives are inferior to solder in both electrical and thermal conductivity. Second, the electronics assembly process requires two steps, one to attach those components that are preferably soldered and one to attach those components which must be adhesively secured.
Disclosures of interest are found in U.S. Pat. Nos. 4,628,422; 4,729,076; 4,742,432; 4,935,665; 5,528,474; 5,632,551; 5,782,555; 5,785,418; 6,016,038; 6,045,240; 6,161,910; 6,435,459; 6,480,389; 6,517,218 and 6,582,100.